Elevator cab doors are opened and closed by moving them back and forth over guide tracks which are mounted on the cab. The door drive systems which are typically used on elevator cabs employ a rotary motor mounted on the roof of the cab, which motor actuates a complicated set of articulated arms which are pivotally connected to the cab doors. When the motor rotates in a first direction, the arms operate to move the doors away from each other so as to open the elevator doors. Rotation of the motor in the opposite direction causes the arms to move the doors toward each other so as to close the elevator doors. The doors are mounted on the guide track by means of rollers which engage the upper surface of the guide track. In order to provide smooth and continuous engagement between the rollers and the guide track as the doors are opened and closed, the articulated arms must be attached to the doors at the center of gravity of the latter. If this parameter is not met, the doors will tend to tilt or rock as they move over the guide tracks, wherein one of the guide rollers may actually be lifted off of the track. This problem is exacerbated in high performance door systems wherein an opening or closing time of less than 1.5 seconds for 1100 mm door openings is the objective. Rocking of the doors during opening and closing is visually unacceptable, and creates undesirable noise levels and cab vibration.